Ionization and Recombination: Laboratory Measurements and Observational Consequences Daniel Wolf Savin Columbia Astrophysics Laboratory 550 West 120th Street MC 5247 New York, NY 10027 Reliably interpreting spectra from both photoionized and electron-ionized cosmic sources requires an accurate understanding of the ionization balance and the underlying atomic collision processes which produce the ionization structure. Uncertainties in ionization balance calculations hamper our ability to model cosmic sources and affect our ability to infer reliably their properties. Of particular importance are accurate rate coefficients for electron impact ionization (EII) and dielectronic recombination (DR) . I will review the astrophysical implications due to current uncertainties in EII and DR and discuss our ongoing laboratory work aimed to remove these uncertainties.